1. Field of the Invention
The subject invention generally pertains to what is known as a multi-panel sliding door and more specifically to an actuator for such a door.
2. Description of Related Art
So-called multi-panel sliding doors include two or more generally parallel door panels that are suspended by carriages that slide or roll along an overhead track. The carriages allow the door panels to travel in a generally horizontal direction in front of a doorway to open and close the door. When the door is open, the door panels generally overlay each other at one side of the doorway. To close the door, the panels slide out from behind each other to move in front of the doorway. When fully extended, the panels cover a span that approaches the sum of their individual widths. Applying such an arrangement to both sides of the doorway provides a bi-parting door with multiple panels on each side. In which case, leading panels (i.e., those first to pass in front of the doorway) from each side meet at generally the center of the doorway when the door closes.
With multi-panel sliding doors, the horizontal translation of a leading door panel is usually powered by a drive unit, while one or more lagging panels are pulled back and forth into position indirectly by somehow being coupled to the driven movement of the leading panel. To do this, often a vertical edge seal, strap or some other coupling connects a lagging panel to a leading one. As the leading panel is driven to move away from the center of the doorway to open the door, the lagging panel may remain stationary in front of the doorway until the leading panel has moved to where it overlays at least most of the lagging one. At this point the leading panel begins pulling the lagging one along with it to one side of the doorway in response to the coupling engaging or tightening rather suddenly. Due to the inertia of the lagging panel, the sudden action of the coupling creates a reaction comparable to that of an impact between the two panels. A similar mechanism may also be employed to pull the lag panel to the closed position.
The impact-like reaction strains the coupling and the points at which the coupling attaches to the panels. This can damage various components of the door or shorten the door""s overall useful life. The impact effect also places a sudden inertial load on the drive unit, which slows the opening of the door.
For doors that are designed to open automatically in the presence of an approaching vehicle, such as a forklift, a slow opening door is susceptible to being struck by a fast moving vehicle. Moreover, a closed door limits a driver""s visibility to only what is in front of the door. The nature of the impact can also lead to a jerky, unsmooth door operation, particularly if the lag panel is freely moveable. Moreover, with a free lag panel, it may be difficult to accurately maintain the lag panel in a desired open or closed position, since it may be subject to drift when not directly engaged by or coupled to the lead panel
To assist in providing smooth door operation and reliable positioning of a lag panel in a multi-panel sliding door, an auxiliary drive is used to move the lag panel.
In some embodiments of a multi-panel sliding door, a primary drive unit moves one panel while an auxiliary drive mechanism that includes a suspended weight moves another panel.
In some embodiments, a primary drive unit moves one panel directly, while moving another panel indirectly by way of an auxiliary drive mechanism that includes a belt, chain or some other flexible ring encircling two rotatable members such as a sheave, sprocket or some other type of wheel, the auxiliary drive being coupled to the driven panel.
In some embodiments, a drive mechanism that includes a belt, chain or some other flexible ring encircling two rotatable members such as a sheave, sprocket or some other type of wheel, also includes a bumper that is attached to the ring and engageable with a stop, wherein the position of the bumper can be varied to allow door panels of a given width to accommodate doorways of different widths.
In some embodiments, a lead and lag panel have a first state where one panel moves independently of the other, and a second state where movement of one panel is dependent on movement of the other panel, with the panels moving at different speeds.
In still other embodiments, lead and lag panels are coupled for movement with a constant speed differential between panels sometime during movement of the panels to an open position.